Drawing of synthetic polymers



y 1963 M. ABBOTT 3,090,077

DRAWING OF SYNTHETIC POLYMERS Filed Feb. 4. 1960 United States Patent 3,90,t)77 DRAWING 6F SYNTi-ETIC PQLYMERS Marl; Abbott, Cornwall, ()ntario, Canada, assignor to Canadian Industries Limited, Montreal, Quebec, Canada, a corporation of Canada Filed Feb. 4, 1960, Ser. No. 6,786 Claims priority, application Great Britain Mar. 13, 1959 4 Claims. (Cl. 118-48) The present invention relates to a new and improved method and apparatus for drawing filaments, yarns, threads, and the like structures composed of synthetic linear polymers.

'Filament yarn made from synthetic linear polymers, such as polyethylene terephthalates, is produced by spinning the molten polymer and then subjecting the filaments so produced to a stretching process to increase, inter alia, their tensile strength, and so provide an article useful in the textile industry. The stretching process, commonly referred to as drawing, requires, in the case of the above mentioned polyesters, the application of heat to the yarn for satisfactory drawing. One way of drawing the yarn is to feed it from a feed roll, at a given rate, to a heated rod (snubbing pin). During its passage around the pin the yarn undergoes a continuous stretching operation. The tension required for the stretching operation is maintained by winding the yarn by means of a draw roll rotating at a faster peripheral speed than the feed roll. As an alternative to this process a heated plate is interposed between the snubbing pin and the draw roll which plate contacts the yarn thereby effecting a socalled secondary draw. Yet another variation of this process uses a rotating hot pin in which the pins peripheral speed is essentially the same as the speed of the undrawn yarn.

It is a disadvantage in all the known hot drawing processes that yarn is obtained which may vary in denier and elasticity along its length sufficiently to affect ad versely the uniformity of woven or knitted fabric and which also has undesirable variability of dye uptake which may, thus, cause pattern effects or streaks in plaindyed fabrics. Moreover, in those processes in which the yarn is drawn over stationary pins and plates some abrasion occurs which causes broken filaments and seriously limits the speed of the drawing process.

It has now been found that the above disadvantages tend to be overcome by the novel arrangement hereinafter to be described. In addition it would also seem likely, that at a level of tenacity comparable to that obtained in those processes in which the yarn is drawn over stationary pins and plates, less shrinkage on boiling in water may be obtained with filamentary material treated according to the process to be defined presently.

According to the present invention there is provided a process for not-drawing filamentary synthetic linear polymers which comprises passing repeatedly the filamentary material around a heated feed roll, thereafter passing the filamentary material over an idler roll and then repeatedly around a heated draw roll arranged coaxially with the feed roll and revolving at a faster peripheral speed than the feed roll, and finally winding up the yarn so drawn.

So that the filamentary material may be passed repeatedly around the feed roll and the draw roll easily it has been found most convenient to associate with each of these rolls a separator roll. This arrangement ensures that the yarn does not contact any stationary surfaces during the drawing operation and thus eliminates 3,%,077 Patented May 21, 1963 ice abrasion. Nevertheless, it may under certain conditions still be desirable to replace the separator roll associated with the feed roll by a stationary cold rod of suitable material. Moreover, it may for certain purposes still be found desirable to use a heated plate, and such a plate may be used in substitution of, or in addition to, the separator roll associated with the draw roll. if a heated plate is used, at say a temperature between 150 and 190 C., the tenacity of especially polyethylene terephthalate filamentary material is improved, but this advantage must be viewed against the abrasion which occurs when the material contacts the stationary surface of the heated plate.

It is preferred that the feed and draw rolls be made from a single piece of heat-conductive material, such as steel, and the unit so obtained is hereinafter referred to as a Uniroll. Such a Uniroll would, therefore, consist of a feed roll of small diameter, conveniently between 2 and 5 cms., projecting coaxially from the draw roll of larger diameter, conveniently between 6 and 30 cms. Alternatively the feed roll and draw roll can, of course, be made separately.

The Uniroll may have a single heater fitted in the feed roll, it may have a single heater fitted in the draw roll, or it may have separate heaters fitted within the feed roll and within the draw roll. In the preferred conditions of the process of the invention the surface of the draw roll is maintained at a higher temperature than the surface of the feed roll. These conditions may suitably be obtained by utilising a single heater, such as an electric element, placed inside the draw roll. By suitable design of the heater and the Uniroll it will so be possible to arrange any desirable temperature differential between the surfaces.

In all hot drawing processes it is desirable to provide control of the temperature of all the heated elements. For example, in the case of polyethylene terephthalate filamentary material suitable feed roll surface temperatures lie between and C. For the same filamentary material the draw roll surface temperature may vary between a wide range in that an elevated temperature of only 50 'C., or even lower, has been found suitable and so has a temperature as high as C. Generally speaking, though, the preferred draw roll temperature will lie between 90 C. and 160 C.

It has been found that excellent temperature control can be achieved by the use of thermistors embedded beneath the surface of the rolls in conjunction with common thermistor control units. If a single heater is employed, it is necessary only to control the surface temperature of the draw roll since, by design, the temperature gradient between the draw roll and the feed roll can be made sufficiently stable to ensure that the temperature of the feed roll surface is acceptable. The thermistors may be connected through slip rings to the control circuit. The heating arrangement may be stationary or may be designed to rotate with the Uniroll by means of, for example, the use of slip rings.

The properties of the filamentary material produced may be varied over a wide range by adjusting the temperatures and/ or the drawspeed and also by altering the string-up arrangements which determine the time of contact of the filamentary material with the heated rolls. Also, by varying the tension of the filamentary material as it finally leaves the draw roll, the physical properties of the filamentary material such as its residual shrinkage and tensile properties may be Varied widely.

A Uniroll according to the present invention is likely to be most useful in the manufacture of drawn yarns having deniers within the range of from 15 to 1100 and with drawing speeds up to 1500 metres/min. Any draw ratio customarily used for the drawing of yarns made of synthetic linear polymers such as polyethylene terephthalate may be used. The preferred draw ratios are in the range 3.6:1 to 4.4:1. It will, however, be appreciated that the draw ratio of a Uniroll is fixed by the ratio of the diameter of the draw roll to that of the feed roll.

In operating the process of the present invention, it is desirable that conditions be chosen so as to ensure that the stage at which drawing occurs, is located at a point just before the yarn leaves the feed roll, in order to minimize relative movement of draw yarn to the feed roll surface.

The accompanying drawing illustrates schematically the preferred process and apparatus for the present invention. Undrawn yarn (Y unwinds freely from a bobbin and passes through a suitable tensioning device (not shown) to the heated feed roll (F). The yarn is passed around the feed roll and the separator roll (I several times and is then passed to the heated draw roll (D) via idler roll (1 After passing around the draw roll (D) and the separator roll (I several times the drawn yarn (Y is taken up on a suitable wind-up device (not shown).

The temperatures of the feed roll (F) and the draw roll (D) may be any temperature known to be suitable for the yarn to be drawn. In the case of polyethylene terephthalate filaments, best results are generally obtained by maintaining the surface of the draw roll at a temperature between 120 and 150 C. and that of the feed roll at a temperature between '80 and 110 C.

The following examples are illustrative of the practice of this invention. All the yarns were polyethylene terephthalate yarns.

EXAMPLE 1 A ISS-denier, 24-filament yarn was passed four times around a feed roll heated to a temperature of 90 C. and its associated separator roll. The feed roll was 2.75 cms. in diameter and was an integral part of a Uniroll consisting of coaxial draw and feed rolls having a ratio of diameters of 3:65. The feed and draw rolls were heated indepently and the temperature of their surfaces was measured with thermistors embedded beneath their respective surfaces. Conduction between the two rolls was minimized by suitable design of a flange connecting the two rolls. Th cheaters rotated with the rolls and were supplied with current through slip rings. Slip rings were also used in the thermistor control circuits. The yarn from the feed roll was passed via an idler roll, situated approx'mately 25 cms. below the feed roll, to the draw roll. After passing around the draw roll and its associated separator roll four times the yarn was wound up on a conventional down-twister spindle. The draw roll surface was controlled at 140 C. and its peripheral speed was 600 metres per minute. Yarn drawn in this way was found to have a denier of 50 corresponding to the imposed draw ratio of 3.65, a tenacity of 5.1 grams per denier, elongation to break of 32% and shrinkage in boiling water of 4.5%. The yarn so drawn was substantially free of defects such as broken filaments, loops and undrawn yarn.

EXAMPLE 2 Undrawn yarn similar to that described by the above example was drawn on the equipment also described in Example 1 at a drawspeed of 400 metres per minute and with a feed and draw roll temperature of 90 and 140 C. respectively. For comparison the same spun yarn was drawn (under optimum conditions for attaining reduced shrinkage) using a conventional heated snubbing pin at 90 C. followed by a hot plate at 165 C. at a drawspeed of 400 metres per minute. Both yarns were wound up on bobbins after drawing. The physical properties of the yarns obtained are table below:

compared in the Table 1 Sample Heated Pin/plate uniroll Denier 50. O 50. 5 Tenacity, grams,denier 5. 10 5.06 Elongation, percent 32.0 31. 5 Shrinkage, percent 4. 5 5. 9

Undrawn yarn similar to that described in the above Example 1 was drawn on the equipment also described in Example 1, at a drawspeed of 600 metres per minute and with a feed and draw roll temperature of C. and 50 C., respectively. Yarn drawn in this way was found to have a denier of 50, a tenacity of 4.68 grams per denier, elongation at break of 34.0% and shrinkage in boiling water of 13.4%.

EXAMPLE 4- A SSO-denier, 24-filarnent yarn was drawn on the same heated Uniroll as that described in Example 1. A drawspeed of 180 metres per minute was used and feed and draw roll temperatures were controlled independently at C. and C. respectively. The yarn drawn on this equipment had a denier of 153, a tenacity of 4.3 grams per denier, elongation 25% and shrinkage 2.1%.

EXAMPLE 5 A SSO-denier, 24-fil-ament yarn was drawn on a heated Uniroll of the same dimensions as that described in EX- ample 1. However, the Uniroll was heated by means of a stationary electric heater situated inside the Uniroll and supplied with current at constant voltage. This heater heated both the feed and the draw roll surfaces, the temperatures of which were measured by means of a surface pyrorneter on stopping the roll. A drawspeed of metres per minute was used and feed and draw roll temperatures were measured as 90 C. and 108 C. respec tively. The yarn drawn on this equipment had a denier of 150, a tenacity of 4.55 grams per denier, elongation 28% and shrinkage 9.0%.

EXAMPLE 6 An MOO-denier, 48-filament yarn was drawn on a heated Uniroll having a feed roll diameter of 2.73 cms. and a draw roll diameter of 12.0 cms. The peripheral speed of the draw roll was 22.0 metres/minute, the feed roll surface temperature was 90 C. and draw roll surface temperature 110 C. The yarn so drawn had a denier of 253.0, a tenacity of 5.8 grams per denier, an elongation at break of 16.6% and a shrinkage in boiling water of EXAMPLE 7 in the yarn. Both yarns were passed through this instrument at a rate of 590 feet per minute and the fault counts over periods of five minutes are set out in the Table II 'below. The results clearly indicate the superior quality of the yarn produced with the heated Umroll process.

Table II Fault Fault Pin and plate counts Heated uuiroll counts sample No. per sample N0. per 5 minutes minutes EXAMPLE 8 An ll00-denier, 48-filarnent yarn was drawn on a heated Uniroll having a feed roll diameter of 2.75 cm. and a draw roll diameter of 12 cms. The peripheral speed of the draw roll was 220 metres/min. The feed roll temperature was 88 C. and the draw roll temperature was 50 C. A hot plate at a temperature of 172 C. was interposed between the feed roll and the draw roll. The drawn yarn obtained had a denier of 243.6, a tenacity of 6.4 grams per denier, an elongation at break of 11.4% and a shrinkage in boiling water of 7.1%.

EXAMPLE 9 A 220-denier, 24-filament yarn was drawn on a heated Uniroll having a feed roll diameter of 2.75 cms. and a draw roll diameter of 12 crns. The peripheral speed of the draw roll was 600 metres/min. The feed roll temperature was 92 C., the draw roll temperature was 50 C. and the temperature of a hot plate interposed between the feed roll and the drawn roll Was 169 C. The drawn yarn obtained had a denier of 49.6, a tenacity of 7.2 grams per denier, and extension at break of 8.2% and a shrinkage in boiling water of 9.25%.

EXAMPLE A 220-denier, 24-filament yarn was drawn on a heated Uniroll having a feed roll diameter of 2.75 cms. and a draw roll diameter of 12 mm. The peripheral speed of the draw roll was 600 metrcs/rnin., the feed roll tempera ture was 92 C., the draw roll temperature was 125 C. and the temperature of a hot plate interposed between the feed roll and the draw roll was 174 C. The denier of the drawn yarn obtained was 52.1, the tenacity 8.1 grams per denier, the elongation at break 10.0% and the shrinkage in boiling water 3.7%.

Many differing embodiments of this invent-ion may be made without departing from the spirit and scope there of. Thus, for example, it is possible to modify within the spirit of the present invention the arrangement hereinhefore illustrated by the use of a nip roll in conjunction with the feed roll or of means allowing the drawn material to be relaxed or causing it to be stretched.

What I claim is:

1. A process for hot-drawing polyethylene terephthalate filamentary material, which comprises passing repeatedly the filamentary material around a feed roll having a surface temperature of from C. to 120 C., thereafter passing the filamentary material over an idler roll and then repeatedly around a draw roll having a surface temperature of from 50 C. to 160 C., said draw roll being arranged coaxially with the feed roll and revolving at a faster peripheral speed than the feed roll, and finally winding up the yarn so drawn.

2. A process according to claim 1 in which the draw ratio is in the range from 3.6:1 to 44:1.

3. A process according to claim 1 in which the draw roll has a surface temperature of from 120 C. to 150 C.

4. A process according to claim 1 in which the feed roll has a surface temperature of from C. to C.

References Cited in the file of this patent UNITED STATES PATENTS 2,182,762 Mengeringhausen et al. Dec. 5, 1939 2,293,995 Muller Aug. 25, 1942 2,533,013 Hume Dec. 5, 1950 2,541,149 Birkenhauer Feb. 13, 1951 2,611,923 Hume Sept. 30, 1952 2,615,784 McClellan Oct. 28, 1952 2,758,908 Kolb Aug. 14, 1956 2,767,429 McCrosky Oct. 23, 1956 2,869,972 Head et a1 Jan. 20, 1959 3,001,236 Maier et a1 Sept. 26, 1961 FOREIGN PATENTS 603,843 Great Britain June 23, 1948 

1. A PROCESS FOR HOT-DRAWING POLYETHYLENE TEREPHTHALATE FILAMENTARY MATERIAL, WHICH COMPRISES PASSING REPEATEDLY THE FILAMETTARY MATERIAL AROUND A FEED ROLL HAVING A SURFACE TEMPERATURE OF FROM 70*C. TO 120*C., THEREAFTER PASSING THE FILAMENTARY MATERIAL OVER AN IDLER ROLL AND THEN REPEATEDLY AROUND A DRAW ROLL HAVING A SURFACE TEMPERATURE OF FROM 50*C. TO 160C., SAID DRAW ROLL BEING ARRANGED COAXIALLY WITH THE FEED ROLL AND REVOLVING AT A FASTER PERIPHERAL SPACED THAN THE FEED ROLL, AND FINALLY WINDING UP THE YARN SO DRAWN. 